package api

import (
	"context"
	"crypto/sha256"
	"database/sql"
	"encoding/hex"
	"net/http"
	"strings"
	"time"

	"git.ryuvia.com/niklas/terdut-server/internal/models"
)

type contextKey string

const (
	ctxUser    contextKey = "user"
	ctxSession contextKey = "session"
)

// AuthMiddleware accepts either of the two credentials the server issues: an
// API key in an Authorization header (the TUI, scripts) or a session cookie
// (the web UI). A request carrying a Bearer header is judged on that alone and
// never falls back to the cookie.
//
// Only the cookie needs a CSRF guard. A browser attaches it to requests other
// sites make, whereas an Authorization header is only ever set by the client
// that holds the key.
func AuthMiddleware(db *sql.DB) func(http.Handler) http.Handler {
	crossOrigin := http.NewCrossOriginProtection()

	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			if header := r.Header.Get("Authorization"); header != "" {
				token, ok := strings.CutPrefix(header, "Bearer ")
				if !ok || token == "" {
					respond(w, http.StatusUnauthorized, errResp("unauthorized"))
					return
				}
				userID, ok := apiKeyUser(r.Context(), db, token)
				if !ok {
					respond(w, http.StatusUnauthorized, errResp("unauthorized"))
					return
				}
				serveAs(w, r, next, db, userID, 0)
				return
			}

			c, err := r.Cookie(sessionCookie)
			if err != nil || c.Value == "" {
				respond(w, http.StatusUnauthorized, errResp("unauthorized"))
				return
			}
			sessionID, userID, ok := sessionUser(r.Context(), db, c.Value)
			if !ok {
				respond(w, http.StatusUnauthorized, errResp("unauthorized"))
				return
			}
			if err := crossOrigin.Check(r); err != nil {
				respond(w, http.StatusForbidden, errResp("cross-origin request rejected"))
				return
			}
			serveAs(w, r, next, db, userID, sessionID)
		})
	}
}

// apiKeyUser resolves an API key to its user and stamps its last use.
func apiKeyUser(ctx context.Context, db *sql.DB, token string) (int64, bool) {
	var keyID, userID int64
	err := db.QueryRowContext(ctx,
		"SELECT id, user_id FROM api_keys WHERE key_hash = $1", hashToken(token),
	).Scan(&keyID, &userID)
	if err != nil {
		return 0, false
	}

	// best-effort; don't fail the request if this update fails
	db.ExecContext(ctx,
		"UPDATE api_keys SET last_used_at = $1 WHERE id = $2",
		time.Now().Unix(), keyID)
	return userID, true
}

// sessionUser resolves a session token to its session and user. The expiry
// slides forward with use, but at most once per sessionTouchEvery, so a page
// that polls does not write to the database on every request.
func sessionUser(ctx context.Context, db *sql.DB, token string) (sessionID, userID int64, ok bool) {
	now := time.Now()
	var lastSeen int64
	err := db.QueryRowContext(ctx, `
		SELECT id, user_id, last_seen_at FROM sessions
		 WHERE token_hash = $1 AND expires_at > $2`,
		hashToken(token), now.Unix()).Scan(&sessionID, &userID, &lastSeen)
	if err != nil {
		return 0, 0, false
	}

	if now.Sub(time.Unix(lastSeen, 0)) > sessionTouchEvery {
		db.ExecContext(ctx,
			"UPDATE sessions SET last_seen_at = $1, expires_at = $2 WHERE id = $3",
			now.Unix(), now.Add(sessionTTL).Unix(), sessionID)
	}
	return sessionID, userID, true
}

// serveAs loads the user and hands the request on with it in the context.
// sessionID is zero for API-key requests.
func serveAs(w http.ResponseWriter, r *http.Request, next http.Handler, db *sql.DB, userID, sessionID int64) {
	var u models.User
	var createdUnix int64
	if err := db.QueryRowContext(r.Context(),
		"SELECT id, username, email, created_at FROM users WHERE id = $1", userID,
	).Scan(&u.ID, &u.Username, &u.Email, &createdUnix); err != nil {
		respond(w, http.StatusUnauthorized, errResp("unauthorized"))
		return
	}
	u.CreatedAt = time.Unix(createdUnix, 0).UTC()

	ctx := context.WithValue(r.Context(), ctxUser, u)
	if sessionID != 0 {
		ctx = context.WithValue(ctx, ctxSession, sessionID)
	}
	next.ServeHTTP(w, r.WithContext(ctx))
}

func hashToken(token string) string {
	h := sha256.Sum256([]byte(token))
	return hex.EncodeToString(h[:])
}

func userFromContext(ctx context.Context) (models.User, bool) {
	u, ok := ctx.Value(ctxUser).(models.User)
	return u, ok
}

// sessionFromContext returns the id of the session a request was authenticated
// with, or false for an API-key request.
func sessionFromContext(ctx context.Context) (int64, bool) {
	id, ok := ctx.Value(ctxSession).(int64)
	return id, ok
}